The optical absorption spectra of infrared stimulable phosphor SrS∶Eu, Sm in the saturated and bleached states of optical storage were investigated. The valence and number of Sm3+ ions were examined via the Sm3+ 4f-4f absorption in near-infrared region. It was found that the broad band absorption corresponding to the transition for electrons stimulated from the traps to the conduction band is decreased at the wavelengths of Sm3+ absorption lines. The dependence of optical storage on Sm concentration was measured. A new trapping mechanism in SrS∶Eu,Sm was presented based on our experimental results and the role of Sm ions was identified.